In a semiconductor memory device, for instance, a NAND flash memory, there is a tendency that capacitive coupling between neighboring cells increases with development in microfabrication of elements. Hence, there is a subject that a threshold voltage of a previously written memory cell varies due to data write of a neighboring cell. To cope with this, a method has been proposed, wherein after data is written in a neighboring cell, write is executed at a final threshold voltage. In this write method, by using a flag cell serving as a memory cell for a flag, it is discriminated whether data write of a second page has been executed. A dummy cell for suppressing a variation in the neighboring cell is disposed adjacent to the flag cell.